Susan M. Escudier, M.D., F.A.C.P. specializes in medical oncology and hematology with special interest in colon cancer. She is board certified in internal medicine, oncology and hematology. Dr. Escudier serves on the Texas Oncology Medical Oncology Quality Committee. Dr. Escudier has received Chief Resident’s Outstanding Medical Resident Award. She is currently a Clinical Associate Professor of Medicine at Baylor College of Medicine and chairs the Granting Committee for the American Cancer Society’s event "Making Strides Against Breast Cancer". She previously served as Assistant Professor at M.D. Anderson Cancer Center where she was involved in Leukemia research.
Fat consumption in the United States is much higher than that needed to meet the physiological needs for energy and essential fatty acids. The average U.S. diet is estimated to contain approximately 37 percent of calories from fat. Dietary recommendations are to decrease total fat intake to 30 percent of calories. The major sources of fat in the American diet are added fats and oils used as spreads, cooking fats, and salad oils as well as the fat in meats and whole milk dairy products.
Because dietary fat intake is highly correlated with calorie intake, the question has been raised as to whether fat intake or calorie intake is the major dietary factor affecting cancer risk. However, the few studies that have addressed the relative importance of fat intake versus calorie intake suggest that both fat and calorie intake have independent effects. Dietary fat is the most concentrated source of energy of all the nutrients and supplies nine calories per gram compared to four calories per gram from either carbohydrate or protein. In general, a reduction in dietary fat intake is accompanied by a decrease in total calorie intake and body weight (Boyd et al., 1990; Henderson et al., 1990).
Dietary Fiber: Dietary fiber falls into two categories, water-soluble fiber and water-insoluble fiber, and is generally defined as those components of food plants resistant to the enzymes produced by the human digestive tract.
Increasing evidence suggests that diets high in fiber-containing foods are associated with a reduced risk for cancer, especially cancer of the colon (Trock et al., 1990). A few studies have also shown a reduced risk for cancers of the breast, rectum, oral cavity, pharynx, stomach, and other sites with diets rich in fruits, vegetables and grain products (Lanza et al., 1992). Because these foods contain other nutrients as well as fiber, and are usually lower in fat, it has not been possible to determine whether the protective effect is attributable to dietary fiber.
Fruits and Vegetables: Populations consuming diets high in fruits and vegetables tend to have a lower cancer risk. Fruits, vegetables, and grains contain a number of nutrients, including carotenoids, vitamin A, and vitamin C. The cancers for which there is evidence of a protective effect include those of the lung, colon and rectum, breast, oral cavity, esophagus, stomach, pancreas, uterine cervix, and ovary. For most cancer sites, especially epithelial cancers of the respiratory and digestive tracts, persons with low fruit and vegetable intake had about twice the risk of cancer as those with high intake (Block et al., 1992).
Carotenoids and Vitamin A: Numerous studies have found evidence that carotenoids reduce the risk of some cancers. The evidence is particularly strong for lung cancer (Ziegler, 1989), even after taking smoking into account. Every study that examined the role of carotene-rich foods found reduced lung cancer risk with higher intake, and about 20 of 25 studies yielded statistically significant results. Five of six studies of blood carotenoids found that persons with higher levels had reduced risk. There is no question that smoking is the strongest risk factor, and quitting smoking is the most important step to reduce risk. It appears, however, that there may be additional benefit to increasing the consumption of foods containing carotenoids.
Carotenoids are found in dark yellow/orange vegetables and fruits such as carrots, sweet potatoes, and cantaloupe and in deep green leafy vegetables such as broccoli, spinach, and collard greens. There are many different carotenoids in such foods, including beta-carotene, alpha-carotene, and lutein.
While the current dietary recommendation is for five servings of fruit and vegetables a day, Americans fall somewhat short of this goal. A recent survey showed that only 23 percent of the population is achieving this goal; the average daily intake is about three and a half servings of fruits and vegetables (Subar et al., 1992).
Vitamin C: Vitamin C is found in fruits, particularly citrus fruits and juices, and in green vegetables, as well as in some fortified foods. Of a group of epidemiologic studies investigating the role of vitamin C, three-fourths found that vitamin C, or fruit rich in vitamin C, provides significant protection (Block 1991). The evidence is most consistent for cancers of the esophagus, oral cavity, and stomach, but protective effects have been reported for cancers of the pancreas, rectum, and cervix. There is increasing evidence for a role in lung cancer, and an analysis combining results of studies of diet and breast cancer found that vitamin C had a strong and significant negative association (Howe et al., 1990).
Other Nutrients: Fruits, vegetables, and grains contain other vitamins and minerals associated with a protective effect against cancer.
Vitamin E has inhibited tumors in experimental animals and been linked to reduced risks of oral, stomach, and other cancer in epidemiologic studies. Selenium also may have a protective effect. In a recent randomized large-population trial testing the effectiveness of vitamin/mineral supplementation among persons in high risk areas of China, those who received daily supplements with a combination of beta-carotene, vitamin E, and selenium for 5 years had a significantly lower cancer death rate (Blot et al., 1993). The findings do not automatically translate to Western populations--in that the Chinese population studied was chronically deficient in a number of nutrients--but offer a hopeful sign that certain vitamins and minerals may lower risk of some cancers. However, two other recent large randomized trials of supplements, one testing the effect of supplemental beta-carotene or alpha-tocopherol in the prevention of lung cancer among smokers and the other testing the effect of supplemental beta-carotene and vitamins C and E in the prevention of adenomatous polyps (a precursor lesion for colorectal cancer), suggest that supplemental use of these nutrients does not reduce the risk of either lung or colorectal cancer (The ATBC Study Group, 1994; Greenberg et al., 1994). In the study of the effect of beta-carotene or alpha-tocopherol on lung cancer among smokers, dietary intake of these nutrients from foods was associated with a reduced risk for lung cancer (The ATBC Study Group, 1994). Some studies suggest that calcium may play a protective role in colon cancer. A 19-year prospective study in men showed the risk for colon cancer was lower in those with the highest calcium intake (Garland, 1985). In addition to dairy products, certain vegetables are good sources of calcium, notably roots, okra, and dark green leafy vegetables such as collard greens.